This invention relates generally to a composition of matter in which resins are polymerizable using polymerizing agents and, more particularly, to compositions that are especially adapted for polyphenylene ether (PPE) and modified PPE resin formulations. These compositions are made into prepreg dielectric sheets or coated on a substrate and cured to form dielectric laminate structures for circuit packaging structures.
One conventional technique for forming laminate circuit structures is to provide a sheet of what is referred to as prepreg, which is glass cloth impregnated with a resin solution which subsequently is either dried or partially cured. Also, a similar type of resin is sometimes used without the glass cloth and coated onto metal, such as copper, for use as build up layers. These are commonly referred to as resin coated copper (RCC) or polymer coated copper (PCC). Such prepregs are then laminated with copper foils forming cores. Cores are then processed further, such as forming vias and circuitry thereon, and then laminated with additional prepregs and copper foils to form a composite laminate structure. Particularly useful resins for forming prepregs are described in U.S. Pat. No. 6,352,782 B2, often referred to as PPE, assigned to General Electric Company, hereinafter sometimes referred to as the GE patent, and in U.S. Pat. No. 5,352,745, often referred to as the modified PPE or APPE, assigned to Asahi Kasei Kogyo Kabushiki Kaisha of Tokyo, Japan, sometimes hereinafter referred to as the Asahi patent. Both of these patents are incorporated herein by reference. The PPE resin as described in the GE patent is a reactively end capped poly(phenylene ether) compound cured with certain unsaturated compounds for synthesizing resins ideally adapted for impregnating fibrous reinforcement in the manufacture of circuit boards. The PPE is described in the Asahi patent as a curable polyphenylene ether resin composition comprising a reaction product obtained by reacting a polyphenylene ether with an unsaturated carboxylic acid or an acid anhydride and at least one cyanurate. Generally speaking, these compositions include about 98% to about 40% by weight of a curable polyphenylene ether resin comprising a reaction product obtained by reacting a polyphenylene ether with an unsaturated carboxylic acid or an acid anhydride, and 2% to 60% by weight, based on the total weight of this and the previous components, of at least one cyanurate selected from the group consisting of triallyl isocyanurate and triallyl cyanurate. These compositions include an initiator. Generally speaking, the initiator is a peroxide of a low molecular weight compound, i.e. below about 700 grams per mole. These peroxides are described in the Asahi patent in column 13, lines 10-23, and in the GE patent, column 12, lines 19-28. An earlier PPE composition is described in U.S. Pat. No. 5,218,030, assigned to Asahi Kasei Kogyo Kabushiki Kaisha of Tokyo, Japan. It describes the use of poly(phenylene ether) containing pendant allyl or propargyl groups, triallylcyanurate or triallylisocyanurate, and optionally an antimony-containing flame retardant. Other formulations replace the antimony flame retardant with bromine containing compounds.
Several problems have been encountered when using the PPE or modified PPE compositions incorporating low molecular weight initiators. (Hereinafter, the term PPE may be used for both PPE and modified PPE.) First, one problem is that the prepreg has component volatility characterized by the volatilization of the low molecular weight peroxide initiators. Second, following lamination, there is a marked out-gassing which has been attributed to the breakdown components of the low molecular weight initiator that do not enter into the reaction and are trapped in the matrix and outgas upon lamination and, third, the inability to laminate the material after the prepreg has been exposed to wet processing. It is believed that this is due to the fact that the low molecular weight initiator is driven off when the prepreg is heated to remove any absorbed water. The first and third of these conditions result in poor cross linking and, thus, degraded material and final structure properties, and the second of these conditions results in a propensity to delamination of the cured prepreg layers. These are problems that need to be solved to improve the commercial viability of the currently available PPE and APPE products.
A prepreg resin comprising:
(a) 98 to 40% by weight based on the total weight of components (a) and (b), of a curable polyphenylene ether resin;
(b) 2 to 60% by weight based on the total weight of components (a) and (b), of at least one cyanurate selected from the group consisting of triallyl isocyanurate and triallyl cyanurate;
(c) a polymerization initiator comprised of a peroxide functionalized polymer, said peroxide functionalized polymer being fragmented by heat to a plurality of free radical moieties, such as t-butoxide moieties, and a relatively inert moiety having a molecular weight greater than about 1,000.
The invention also encompasses a cured resin ether as a coating on a substrate, without fiberglass cloth embedded, or a cured prepreg with fiberglass cloth embedded and a method of forming the same, and an electronic packaging structure.